1. Field of the Invention
The present invention concerns thiophosphate-containing biocide preparations, and, more particularly, agricultural formulations of biocidal thiophosphate that have a reduced tendency to emit sulfurous vapors.
2. Description of the Related Art
Organothiophosphate compounds refer generally to those containing carbon-phosphorus bonds in which the phosphorus component is also bonded to one or more sulfur atoms. Many of these compounds function as pesticides. Hence, Organothiophosphate insecticides are well known and widely used for crop protection. Included among these compounds are, for example, the commercially available preparations of bensulide known under the trademarks Bensumec™, Betamec™, Betasan™, Disan™, Exporsan™, Prefar™, Pre-San™, and others.
Unfortunately, the organothiophosphate-type insecticides typically contain sulfhydryl compounds, such as thiols or mercaptans, that produce a well known and irritating sulfurous (i.e., “rotten egg”) odor. The presence of compounds such as mercaptans in formulations of these insecticides is due to a number of factors. In some instances, thiophosphate analogs of the organothiophosphate compound are present as by-products of the synthesis, with these analog species tending to decompose to mercaptans. Moreover, organothiophosphate compounds tend to degrade or decompose over time to produce mercaptans, particularly when subjected to heating. Regardless of how the sulfhydryl odor is produced, it is detrimental from an environment point of view, as well as from handling and field application perspectives.
Bensulide technical (S—(O, O-diisopropyl phosphorodithiotate) ester of N-(2-mercaptoethyl) benzenesulfonamide) is the active ingredient in several organothiophosphate pesticide formulations. Bensulide technical is synthesized at a purity range from 92.0% to 95.0%. The remaining 6% percent are process impurities, with some of these impurities being mercaptans and sulfides produced from the reaction of the dithiophosphoric acid.
Bensulide is not considered to be a very stable compound. Indeed, bensulide undergoes an autocatalytic decomposition such that, after 10-20% of the material has decomposed, a large increase in decomposition rate occurs. Decomposition products are known to be mercaptans and sulfides.
Impurities in bensulide have been purged and trapped for analysis by gas chromatography/mass spectrometry (for example, see Bobbi Kahn, Analysis & Certification of Product Ingredients in Betasan, Stauffer Chemical Company, Richmond Research Center (RCC-9/2/86 86-88). The largest impurity was identified as hydrogen sulfide (H2S) and was the only impurity in the headspace analysis that was not found in the actual bensulide composite sample.
Although there are a number a ways known in the art to control various chemical odors, there are often unknown or unwanted chemical changes or other side effects that occur. Moreover, many methods are time consuming, involve hazardous materials, and are relatively expensive to carry out on commercially useful scales, especially when filtration/separation and disposal costs are considered. Thus, there remains a need in the art for new and improved ways for controlling odor in organothiophosphate formulations.